Patterns of myosin isoforms in mammalian skeletal muscle fibres

Abstract

The present article attempts to combine existing information on the distribution of fast and slow myosin isoforms in histochemically distinct muscle fibres. Four myosin heavy chain (MHC) isoforms, MHCI, MHCIIa, MHCIIb, and MHCIId(x), have been identified in small mammals and have been assigned to the histochemically defined fibre types I, IIA, IIB, and IID(X), respectively. These fibres express only one MHC isoform and are called pure fibre types. Hybrid fibres expressing two MHC isoforms are regarded as transitory between respective pure fibre types. The existence of pure and hybrid fibres even in normal muscles under steady state conditions creates a spectrum of fibre types. The multiplicity of fibre types is even greater when myosin light chains are taken into account. A large number of isomyosins results from the combinatorial patterns of various myosin light and heavy chains isoforms, further increasing the diversity of muscle fibres. As shown by comparative studies, the distribution of different fibre types varies in a muscle-specific, as well as a species-specific manner.

Immunohistochemical Classification of Skeletal Muscle Fibers.

“…Single fiber electrophoretic studies support the coexistence of multiple MHC isoforms in individual fibers [51,93]. Previous studies have shown that the hybrid fiber is not an exception but exists as a standard [36,56,69].…”

“…It should be noted that the electrophoretic mobility shows interspecies differences even within identically labeled isoforms [36]. Single fiber electrophoretic studies support the coexistence of multiple MHC isoforms in individual fibers [51,93].…”

Muscle fibre ontogenesis in farm animal species

“…The major MHC isoforms determine the contractile properties of a fibre. The diversity of these isoforms is due to their specific actin-activated and Ca 2+ -stimulated ATPase activities which reside in the head region of the heavy chain [34]. In mammals, slow twitch fibres contain the slow "MHC I" which corresponds to the cardiac beta myosin heavy chain.…”

“…Examples of this can be found in humans [42], bovines [65], rats [91], and horses [70]. These hybrid fibres contain at least two MHC isoforms [34]. Schiaffino and Reggiani [79] also described IIA/IIX fibres, and also observed that different isoforms can be expressed simultaneously in some muscle fibres during foetal life.…”

Adeno-associated virus-mediated gene transfer of the heart/muscle adenine nucleotide translocator (ANT) in mouse

“…However, AAV-ANT1 transduction had no apparent influence on myofiber size or MHC expression pattern (data not shown). 22 Therefore, transduction of Ant1 into ANT1-deficient muscle dramatically improved the muscle pathology associated with this ANT1 enzyme defect.…”